Wearable GTC Seizure Monitor Passes Phase III Test

But prototype had ergonomic issues that developer hopes to resolve.

by John Gever John Gever,Managing Editor, MedPage Today
April 21, 2015

Action Points

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

A multicenter phase III clinical trial tested a small device worn on the arm to detect generalized tonic-clonic seizures in a population of children and adults with treatment-resistant epilepsy.

The monitor captured 100% seizures with a low false-positive rate when worn appropriately, but only 33% when improperly placed, and only 88 of the 147 patients had proper placement of the device throughout the study.

WASHINGTON -- A prototype wearable monitor for detecting onset of generalized tonic-clonic (GTC) seizures at home or in the hospital showed good results in a phase III trial, researchers reported here, but the developer said the device's design needs improvement before it could be brought to market.

For study participants who were able to keep the arm-worn electromyographic sensor properly placed, 100% of GTC seizures were successfully detected with a false-alarm rate of about 1.7 per day, reported José Cavazos, MD, PhD, of the University of Texas Health Science Center in San Antonio, in a presentation at the American Academy of Neurology annual meeting.

But of 147 patients enrolled in the study, only 88 had proper placement of the device throughout the study, and 17 discontinued before completing the study because of discomfort, irritation, or injury from the device.

Cavazos, who is also a co-founder of the commercial firm developing the system, Brain Sentinel, said a smaller unit and new instructional materials had been developed that would help patients place the device correctly to improve detection.

The principal behind the device is that muscular activity at GTC seizure onset has a unique electromyographic signal that can be distinguished from other types of voluntary and involuntary movement. A phase II study reported in 2013 supported the concept. When triggered, the device emits a loud audio alarm and also transmits wirelessly to a laptop computer base station, which also sounds an audio alarm and can send alerts over the Internet.

The system's sensitivity is adjustable, such that the likelihood of detecting a GTC seizure is increased though at a cost of increased false alarms.

Although the system does not give a great deal of advance warning -- it sounds an alert on average 14 seconds into the tonic phase of a GTC seizure -- it may give patients enough time to protect themselves from serious injury. The alert may also allow family members or caregivers to provide timely aid.

It also stores data that could be used retroactively to analyze seizure activity and to improve the system's detection algorithm.

For the current study, Cavazos and colleagues enrolled 147 patients with established epilepsy at 11 U.S. centers, of whom 136 had evaluable electromyographic data (104 adults, 27 adolescents, five children) totaling 7,866 hours. All had treatment-resistant epilepsy with averages of 12, 9, and 22 seizures of all types per month in adults, adolescents, and children, respectively.

In the intent-to-monitor group of 136, there were 40 GTC seizures as adjudicated by neurologists using video EEG recordings, of which 28 were detected by the device. However, 18 of those seizures occurred in participants for whom the device was improperly placed. All 22 GTC seizures that occurred when devices were placed correctly were detected, the researchers determined.

The adjustable sensitivity threshold to trigger the alarm ranged from 95 to 255 (arbitrary units). At a setting of 215 with proper placement, the diagnostic sensitivity was about 95% with a false-alarm rate of 0.04 per hour, or about 1 per day.

At a setting of 145, GTC seizure sensitivity with proper sensor placement was 100%, with a false-positive rate was 0.07 per hour, which the team determined was optimal in that sensitivity is most important for the indication. Cavazos indicated that this was the optimal setting, although patients will -- if the device is approved -- probably be instructed to adjust the setting up or down by as much as 40 points to achieve their own best balance of sensitivity and specificity.

Brain Sentinel's Luke Whitmire, PhD, told MedPage Today that one problem with the prototype was its weight -- at 400 grams, it was bulky and uncomfortable.

A newer model weighing less than 200 grams, and which includes a "cancel" button to prevent false alarms, has been developed, he said.

But Jeff Jung, the firm's vice president for marketing, told MedPage Today in an email that the main issue behind the incorrect placement in many participants was that they put it on the wrong spot. Ideally it should be positioned on the bicep muscle, he explained, but some patients apparently did not understand that.

After discovering the problem on video recordings during the trial, Jung said, "[w]e took corrective action to improve the instructional materials and retrain all of the sites in the first half of 2014. The placement of the device was correct every time after that."

Cavazos said the system is currently under FDA review, although he didn't give a timeline for a final decision.

UPDATE: This article, originally published 4/23/15, was updated with new material Friday, 4/24/15, at 10:30 ET.

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